More than 90% of women in substance use treatment report history of physical and/or sexual trauma, and up to 60% meet criteria for both substance use disorder (SUD) and Post Traumatic Stress Disorder (PTSD). PTSD typically precedes onset of SUD, with substances used as a means to cope with physiological, psychological, and emotional symptoms resulting from the trauma. Women with PTSD experience greater severity of addiction symptoms, readmit into treatment more frequently than women without PTSD, and tend to have poorer treatment outcomes. Due to increased risk for risk and exacerbation of PTSD on SUD severity and treatment success, and the specific vulnerabilities and needs of women with this comorbidity, SUD treatments that target both substance use and trauma recovery are needed. However, few interventions target both SUD and PTSD concurrently, and fewer still are specific to women; most of the existing treatment models have been validated on males or veteran populations. Mindfulness-Based Relapse Prevention (MBRP) has been shown to decrease craving, relapse rates, and quantity/frequency of use across several substances, and has shown acceptability in diverse populations, including ethnic minority women, women offenders, and incarcerated individuals. MBRP integrates mindfulness practices with cognitive behavioral and exposure-based approaches to increase self-regulatory skills while experiencing triggers previously associated with substance use, including challenging affective states such as those common to experienced trauma. Adapting MBRP to incorporate trauma education and treatment approaches has the potential to effectively treat women with the dual vulnerabilities of trauma history and SUD. The current study is thus designed to determine feasibility, acceptability, and initial efficacy of an adapted Trauma-Informed Mindfulness-Based Relapse Prevention (TI-MBRP) intervention for women in substance use treatment settings who have PTSD. TI-MBRP integrates trauma education and treatment approaches drawn from Cognitive Processing Therapy (CPT), an evidence-based intervention for PTSD, into the standard MBRP protocol to provide a trauma-informed approach to treating women in community-based substance use treatment settings. The current proposal will evaluate TI-MBRP, using a randomized, pre-post design, with 80 women in residential substance abuse treatment. Participants will be randomly assigned to participate in an 8- week TI-MBRP intervention or to continue with treatment as usual (TAU). Assessments will be collected pretest, posttest, and at one-month follow-up. It is hypothesized that participants in TI-MBRP, relative to those in TAU, will have greater reductions in craving, substance use, PTSD symptoms, reactivity to negative affect, and experiential avoidance, as well as greater improvements in heart rate variability, self-efficacy, mindfulness, and coping resources. Data from this study will lay the groundwork for a larger scale clinical trial to determine the efficacy of TI-MBRP.